»yamldecode Function

yamldecode parses a string as a subset of YAML, and produces a representation of its value.

This function supports a subset of YAML 1.2, as described below.

This function maps YAML values to Packer language values in the following way:

YAML typePacker type
!!strstring
!!floatnumber
!!intnumber
!!boolbool
!!mapobject(...) with attribute types determined per this table
!!seqtuple(...) with element types determined per this table
!!nullThe Packer language null value
!!timestampstring in RFC 3339 format
!!binarystring containing base64-encoded representation

The Packer language automatic type conversion rules mean that you don't usually need to worry about exactly what type is produced for a given value, and can just use the result in an intuitive way.

Note though that the mapping above is ambiguous -- several different source types map to the same target type -- and so round-tripping through yamldecode and then yamlencode cannot produce an identical result.

YAML is a complex language and it supports a number of possibilities that the Packer language's type system cannot represent. Therefore this YAML decoder supports only a subset of YAML 1.2, with restrictions including the following:

  • Although aliases to earlier anchors are supported, cyclic data structures (where a reference to a collection appears inside that collection) are not. If yamldecode detects such a structure then it will return an error.

  • Only the type tags shown in the above table (or equivalent alternative representations of those same tags) are supported. Any other tags will result in an error.

  • Only one YAML document is permitted. If multiple documents are present in the given string then this function will return an error.

»Examples

> yamldecode("{\"hello\": \"world\"}")
{
  "hello" = "world"
}

> yamldecode("true")
true

> yamldecode("{a: &foo [1, 2, 3], b: *foo}")
{
  "a" = [
    1,
    2,
    3,
  ]
  "b" = [
    1,
    2,
    3,
  ]
}

> yamldecode("{a: &foo [1, *foo, 3]}")

Error: Error in function call

Call to function "yamldecode" failed: cannot refer to anchor "foo" from inside
its own definition.

> yamldecode("{a: !not-supported foo}")

Error: Error in function call

Call to function "yamldecode" failed: unsupported tag "!not-supported".

»Related Functions

  • jsondecode is a similar operation using JSON instead of YAML.
  • yamlencode performs the opposite operation, encoding a value as YAML.